ES2405842T3 - Method and arrangement in a load column - Google Patents

Abstract

Method for reducing the evaporation of volatile organic compounds (VOCs) or other gases during the filling of an essentially liquid petroleum product in a transport or storage tank (2) comprising a loading column (8) through a pipe ( 6) feed, characterized in that the petroleum product is discharged from the feed pipe (6) into the load column (8), the load column (8) having a cross section significantly larger than that of the pipe (6) power.

Description

Method and arrangement in a load column.

This invention relates to a method of reducing the proportion of volatile organic compounds (VOCs) that is separated from oil, in particular crude oil, during tank filling, such as during the loading of a ship from a terminal, a platform production or a floating loading device. The invention also comprises an arrangement for carrying out the method. The arrangement can also be used to reduce the evaporation of gas during the filling of individual components such as propane, butane, ethane and liquefied natural gas.

WO 97/14646 shows a method and arrangement for filling tanks.

Crude oil consists of different stabilized components at a specified pressure and at a specified temperature. If these conditions are altered, through either a reduction in pressure or an increase in temperature, a proportion of the volatile components will be separated and gasified. These components consist of volatile organic compounds such as methane, propane, butane and ethane, and are called VOCs. Currently there are systems for the removal of these gases. Opposite to the provision of the present application, the current systems are based on treating the gases already separated by providing a process arrangement for the treatment of the exhaust gas after evaporation. The plants are complex and will require a lot of energy, since pressure and temperature are used to return the gases to a liquid state.

It is known that a relatively large amount of volatile organic compounds evaporates during the pumping of oil into large tanks. Under normal circumstances, a pressure of the order of 1.05 to 1.07 bar is maintained in both the transport and storage tanks. When a tanker is loaded, for example, it is usual to pump the oil from a storage tank through a feed pipe to a position above the cargo tank, from which the oil is sent inside the tank to through a downpipe (vertical downpipe) to the bottom of the tank. A downstream pipe of this type can have a length of the order of several tens of meters.

When oil flows into the upper end part of the downstream pipeline, gravity will accelerate the liquid that flows down through the downstream pipeline, creating a lower static pressure in the feed pipe and the part top of the downstream pipe. In these pipes, in which the static pressure is lower than the vapor pressure, the evaporation of volatile organic compounds is significant, and only a small part of these compounds will condense back to a liquid state after the tank pressure is restored. normal.

The object of the invention is to remedy the disadvantages of the prior art.

The objective is achieved according to the invention by the features set forth in the following description and in the appended claims.

There are experiments that have shown that if the incoming fluid is passed into an adapted hollow column located in or in connection with the transport / storage tank, the evaporation of gas from the fluid is considerably reduced.

The hollow column is formed as a vertical load column, preferably with a tangential inlet near the upper end part and an outlet near the lower end part. The outlet discharges to the bottom or to the piping system of the transport / storage tank and will be immersed, after the entry of fluid, into the contents of the transport / storage tank without subjecting the fluid to any significant depression.

As the incoming fluid descends from the inlet at the top of the load column to the bottom of the load column, or possibly to a level corresponding to the level of fluid in the transport / storage tank, evaporation takes place Initial gas of the incoming fluid. In a load column of the requested type, the incoming fluid is not subjected to a decrease in static pressure similar to that experienced when it flows down a downstream pipe, as usually happens when the prior art is used. After a period of relatively short inflow, the atmosphere in the loading column is saturated with gas that has evaporated from the incoming fluid, after which any additional evaporation will be insignificant.

The so-called Froude number is known from the theory of open channel hydraulics. The Froude number ß, which is dimensionless, is defined as a quotient between the force of inertia and the force of gravity acting on a fluid:

By substituting the hydraulic depth hm in the formula for the diameter D of the load column, an expression is obtained which has been proven appropriate to select a suitable load column diameter.

The development work carried out has shown that evaporation is reduced when the value of the expression

It is less than 0.45. For 0.31, the pressure in the column will be balanced. The best effect is achieved for values below 0.18.

Therefore, the diameter of the loading column depends mainly on the velocity of the incoming fluid.

10 Advantageously, the upper part of the loading column can communicate, preferably through at least one pressure relief valve, with the transport / storage tank being filled, or with another tank. Therefore, any overpressure or depression in the loading column can be evacuated or equalized by transporting gas between the loading column and the corresponding tank.

Advantageously, the output of the load column is designed according to known fluid flow laws to ensure

15 a laminar flow, and also to ensure that the outlet is submerged in the incoming fluid after having filled a relatively small amount of fluid in the transport / storage tank.

The method and arrangement according to the invention are very suitable for use during loading ships and other large tank parks when it comes to substantially liquid petroleum products.

A non-limiting example of a preferred arrangement and method illustrated in the accompanying drawing 20 is described below, in which:

Figure 1 schematically shows a section of a loading arrangement in which oil is pumped aboard an tanker equipped with a loading column. A spiral endowed with arrows indicates the flow path of the oil in the load column, while the ellipses, also endowed with arrows, indicate a possible flow path for the gas in the load column.

25 In the drawing, reference number 1 designates a ship with a transport tank 2 for oil. When empty, the ship 1 floats relatively high in the water 4. The oil flows from a pumping station (not shown) through a loading pipe 6, tangentially into the upper end part 10 of a column 8 loading The cross section of the load column 8 is significantly larger than that of the load pipe 6. The load pipe 6 may be in the form of, for example, a pipe, a hose or another

30 suitable hollow body.

In this preferred embodiment, the load column 8 constitutes a part of the transport tank 2 on board the ship 1 and has been formed as a cylindrical silo, its upper end part 10 being equipped with a cover 12, and its part 14 bottom end equipped with an outlet 16 that discharges into the transport tank 2.

The upper part 10 of the load column 8 is connected to and in communication with the transport tank 2 to

35 through bifurcation pipes 18 and 20, as well as valves 22 and 24. The pressure relief valve 22 is designed to open for flow from the load column 8 to the cargo hold 2 at a predetermined differential pressure, while the pressure relief valve 24 is designed to open for flow from the cargo hold 2 to the load column 8 at a predetermined differential pressure.

Petroleum containing relatively volatile components is pumped through the load pipe 6 inside

40 of the upper end part 10 of the load column 8, where, due to the tangential connection of the feed pipe 6 to the load column 8, it adopts a helical flow pattern down through the column 8 of load. In figure 1, the flow is illustrated by means of a spiral line with arrows.

The oil then flows through an opening 16 in the lower end part 14 of the loading column 8, the opening 16 near the bottom of the transport tank 2 being terminated. To prevent eddies from occurring in

45 the opening 16, means can be installed to prevent this near the opening 16. Advantageously, the opening 16 is designed to be submerged after a relatively small amount of oil 17 has been pumped into the transport tank 2.

When the first quantity of oil is pumped, some of the most volatile components of oil evaporate during the flow of oil through the loading column 8. After having pumped an amount It is assumed that the gases present in the load column during loading are moving. The ellipses with arrows in Figure 1 illustrate a possible flow path.

The favorable effect of the invention does not depend on the load pipe 6 being connected to the load column 8 tangentially, but there are experiments showing that such geometry is favorable.

Claims (7)

one.

Method for reducing the evaporation of volatile organic compounds (VOCs) or other gases during the filling of an essentially liquid petroleum product in a transport or storage tank (2) comprising a loading column (8) through a pipe ( 6) feed, characterized in that the petroleum product is discharged from the feed pipe (6) into the load column (8), the load column (8) having a cross section significantly larger than that of the pipe (6) power.

2.

Method according to claim 1, characterized in that the petroleum product is guided tangentially into the load column (8).

3.

Arrangement for reducing the evaporation of volatile organic compounds (VOCs) during the filling of an essentially liquid petroleum product in a transport or storage tank (2), the arrangement comprising a feed pipe (6) and a tank (2) of transport or storage comprising a loading column (8), characterized in that the supply pipe (6) has its discharge opening in the upper end part (10) of the loading column (8), the cross section being of the load column (8) significantly larger than that of the feed pipe (6), the load column (8) having its discharge opening (16) in its lower end part (14).

Four.

Arrangement according to claim 3, characterized in that the supply pipe (6) is connected to the load column (8) in an essentially tangential manner.

5.

Arrangement according to one or more of claims 3 to 4, characterized in that the loading column (8) is mainly placed in a storage or transport tank (2).

6.

Arrangement according to one or more of claims 3 to 5, characterized in that the loading column (8) has an opening (16) that discharges near the bottom of the storage or transport tank (2).

7.

Arrangement according to one or more of claims 3 to 6, characterized in that the upper end part (10) of the loading column (8) is connected to the storage or transport tank (2) communicatingly.